JUC并发编程狂神说笔记(超详细)

JUC

环境准备

新建maven项目

  • 使用jdk8,项目中要用到新特性

  • 查看官方文档学习
    JUC并发编程狂神说笔记(超详细)
    JUC并发编程狂神说笔记(超详细)
    JUC并发编程狂神说笔记(超详细)

  • 导入lombok

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.8</version>
        </dependency>

线程和进程

什么是juc
JUC并发编程狂神说笔记(超详细)
Runnable没有返回值,企业中用Callable
java默认有两个线程:main ,GC
线程:开了一个进程TYpora,写字,自动保存(线程负责)
java真的可以开启线程吗?不可以
private native void start0();
//本地方法,调用底层c++,java运行在虚拟机之上,无法直接操作硬件,由c++开启多线程
JUC并发编程狂神说笔记(超详细)
8核心
并发编程的本质:充分利用cpu资源

package com.fang.demo0;

public class Test1 {
    public static void main(String[] args) {
        //获取cpu的核数
        //cpu密集型,io密集型
        System.out.println(Runtime.getRuntime().availableProcessors());
    }
}

查看源码Thread.State

线程的状态:6个
public enum State {
//就绪
NEW,
//运行
RUNNABLE,
//阻塞
BLOCKED,
//等待
WAITING,
//超时等待
TIMED_WAITING,
//终止
TERMINATED;
}

wait与sleep的区别

  1. 来自不同的类
    wait=》Object
    sleep=》Thread
  2. wait释放锁,sleep抱着锁睡觉
  3. wait必须在同步代码快中,sleep可以在任何地方睡觉
  4. wait不需要捕获异常,sleep需要捕获异常(可能发生超时等待)

lock锁(重点)

传统的Synchronized锁

不加Synchronized
package com.fang.demo0;

/**
* 真正的多线程开发
* 线程就是一个资源类,没有任何附属的操作
*/

public class SaleTicket {
   public static void main(String[] args) {
       Ticket ticket = new Ticket();
       //Runnable接口为函数式接口
       new Thread(()->{
           for (int i = 0; i < 40; i++) {
               ticket.sale();
           }
       },"a").start();
       new Thread(()->{
           for (int i = 0; i < 40; i++) {
               ticket.sale();
           }
       },"b").start();
       new Thread(()->{
           for (int i = 0; i < 40; i++) {
               ticket.sale();
           }
       },"c").start();
   }
}
//资源类oop编程
class Ticket {
   //属性,方法
   private int number = 50;
   //买票的方式
   public void sale() {
       if (number>0) {
           System.out.println(Thread.currentThread().getName()+"卖出了"+(number--)+"票,剩余:"+number);
       }
   }
}

买票结果混乱
JUC并发编程狂神说笔记(超详细)
加了锁后正常

    public synchronized void sale() {
        if (number>0) {
            System.out.println(Thread.currentThread().getName()+"卖出了"+(number--)+"票,剩余:"+number);
        }
    }

Lock锁(接口)

默认非公平锁:十分不公平可以插队
公平锁:先来后到
JUC并发编程狂神说笔记(超详细)
加锁

class Ticket {
   //属性,方法
   private int number = 50;
   Lock lock = new ReentrantLock();

   //买票的方式
   public  void sale() {
       lock.lock();//加锁

       try {
           //业务代码
           if (number>0) {
               System.out.println(Thread.currentThread().getName()+"卖出了"+(number--)+"票,剩余:"+number);
           }
       } catch (Exception e) {
           e.printStackTrace();
       } finally {
           lock.unlock();//解锁
       }
   }
}

Sychronized和lock的区别

1.Sychronized 内置的java关键字,Lock锁是一个java类
2.Sychronized 无法判断获取锁的状态,Lock锁可以判断是否获取到了锁.
3.Sychronized 会自动释放锁lock必须手动释放锁,如果不释放锁,死锁
4.Sychronized 线程一(获得锁,阻塞),线程二(等待,傻傻的等),Lock锁就不一定会等待下去.
5.Sychronized 可重入锁,不可以中断,非公平;Lock,可重入锁,可以中断锁,非公平(可以自己设置)
6.Sychronized 适合锁少量的代码的同步问题,Lock适合锁大量的代码同步问题.

锁是什么,如何判断锁的是谁

生产者和消费者的问题

面试:单例模式,排序算法,生产者消费者,死锁

Sychronized版

package com.fang.product;

/**
 * 线程间的通信问题:生产者和消费者的问题!  等待唤醒 通知唤醒
 * 线程交替执行  A B同时操作一个变量
 * A num+1
 * B num-1
 */
public class A {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"A").start();
//        new Thread(()->{
//            for (int i = 0; i < 10; i++) {
//                try {
//                    data.increment();
//                } catch (InterruptedException e) {
//                    e.printStackTrace();
//                }
//            }
//        },"C").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"B").start();
    }
}
//等待 业务 通知
class Data{//数字 资源类
    private int num = 0;
    public synchronized void increment() throws InterruptedException {
        if (num != 0){
            //等待
            this.wait();
        }
        num++;
        System.out.println(Thread.currentThread().getName()+">="+num);
        //通知其他线程,我加一完毕了
        this.notifyAll();
    }

    public synchronized void decrement() throws InterruptedException {
        if (num == 0){
            this.wait();
        }
        num--;
        System.out.println(Thread.currentThread().getName()+">="+num);
        //通知其他线程,我减一完毕
        this.notifyAll();
    }

}

JUC并发编程狂神说笔记(超详细)
加入C线程,执行结果
JUC并发编程狂神说笔记(超详细)
存在问题虚假唤醒
将if改成while防止虚假唤醒.
JUC并发编程狂神说笔记(超详细)

guc版生产者消费者问题

代码实现

package com.fang.product;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class B {
    public static void main(String[] args) {
        Data2 data2 = new Data2();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data2.increment();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data2.increment();
            }
        },"C").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data2.decrement();
            }
        },"B").start();
    }
}
class Data2{//数字 资源类
    private int num = 0;
    Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();
//    condition.await()等待 condition.signalAll()唤醒全部
    public void increment()  {
        lock.lock();
        try {
            //业务代码
            while (num != 0){
                condition.await();
            }
            num++;
            System.out.println(Thread.currentThread().getName()+">="+num);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void decrement() {
        lock.lock();
        try {
            //业务代码
            while (num == 0){
                condition.await();
            }
            num--;
            System.out.println(Thread.currentThread().getName()+">="+num);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

}

JUC并发编程狂神说笔记(超详细)
线程状态随机
想要的执行循序A->B->C

condition实现精准通知唤醒

package com.fang.product;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A->B->C
 */
public class C {
    public static void main(String[] args) {
        Data3 data3 = new Data3();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printA();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printB();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                data3.printC();
            }
        },"C").start();
    }
}
class Data3{
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();
    private int num =1; //1A,2B,3C
    public void printA() {
        lock.lock();
        try {
            //业务,判断,执行,通知
            while (num != 1){
                condition1.await();
            }
            System.out.println("aaaaaaaaaaaa");
            //唤醒指定的人,B
            num =2;
            condition2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printB() {
        lock.lock();
        try {
            while (num != 2){
                condition2.await();
            }
            System.out.println("bbbbbbbbbbbb");
            //唤醒指定的人,B
            num =3;
            condition3.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public void printC() {
        lock.lock();
        try {
            while (num != 3){
                condition3.await();
            }
            System.out.println("ccccccccccc");
            //唤醒指定的人,B
            num =1;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

JUC并发编程狂神说笔记(超详细)

8锁现象彻底理解锁.

什么是锁,锁到底锁的是谁

package com.fang.lock8;

import java.sql.Time;
import java.util.concurrent.TimeUnit;

/**
 * 8锁,就是关于锁的8个问题
 * 1.标准情况下是先发短信还是打电话
 * 2.发短信方法延迟4秒
 */
public class Test1 {
    public static void main(String[] args) {
        Phone phone = new Phone();
        new Thread(()->{
            phone.sendSms();
        },"A").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new Thread(()->{
            phone.call();
        },"B").start();
    }
}
class Phone{
    //synchronized锁的对象是方法的调用者
    //两个方法用的是同一个锁,谁先拿到谁先执行
    public synchronized void sendSms() {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sendSms");
    }
    public synchronized void call() {
        System.out.println("call");
    }
}

package com.fang.lock8;

import java.sql.Time;
import java.util.concurrent.TimeUnit;

/**
 * 3.增加一个普通方法,是先执行发短信还是hello(1秒钟输出hello,4秒后输出发短信)
 * 4.两个对象,两个同步方法,先打电话,再发短信(两个不同的对象,两把锁)
 */
public class Test2 {
    public static void main(String[] args) {
        Phone2 phone = new Phone2();
        Phone2 phone2 = new Phone2();
        new Thread(()->{
            phone.sendSms();
        },"A").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new Thread(()->{
            phone2.call();
        },"B").start();
    }
}
class Phone2{
    //synchronized锁的对象是方法的调用者
    //两个方法用的是同一个锁,谁先拿到谁先执行
    public synchronized void sendSms() {
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sendSms");
    }
    public synchronized void call() {
        System.out.println("call");
    }
    //这里没有锁,不是同步方法,不受锁的影响
    public void hello() {
        System.out.println("hello");
    }
}


package com.fang.lock8;

import java.sql.Time;
import java.util.concurrent.TimeUnit;

/**
 * 5.增加两个静态同步方法,只有一个对象(先发短信,再打电话)
 * 6.两个对象,增加两个静态同步方法(先发短信,再打电话)
 */
public class Test3 {
    public static void main(String[] args) {
        //两个对象的class模板只有一个,static,锁的是class
        Phone3 phone = new Phone3();
        Phone3 phone2 = new Phone3();
        new Thread(()->{
            phone.sendSms();
        },"A").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new Thread(()->{
            phone2.call();
        },"B").start();
    }
}
class Phone3{
    //synchronized锁的对象是方法的调用者
    //static 静态方法 类一加载就有了!class模板,锁的是class对象Class<Phone3> phone3Class = Phone3.class;
    //两个方法用的是同一个锁
    public static synchronized void sendSms() {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sendSms");
    }
    public static synchronized void call() {
        System.out.println("call");
    }
}

package com.fang.lock8;

import java.sql.Time;
import java.util.concurrent.TimeUnit;

/**
 * 7.一个静态同步方法,一个普通的同步方法,一个对象(先打电话)
 * 8.两个对象(先打电话)
 */
public class Test4 {
    public static void main(String[] args) {
        //两个对象的class模板只有一个,static,锁的是class
        Phone4 phone = new Phone4();
        Phone4 phone2 = new Phone4();
        new Thread(()->{
            phone.sendSms();
        },"A").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new Thread(()->{
            phone2.call();
        },"B").start();
    }
}
class Phone4{
    //锁的是class类模板
    //static 静态方法 类一加载就有了!class模板,锁的是class对象Class<Phone3> phone3Class = Phone3.class;
    //两个方法用的是同一个锁
    public static synchronized void sendSms() {
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sendSms");
    }
    //普通的同步方法,锁的是调用者
    public synchronized void call() {
        System.out.println("call");
    }
}


CopyOnWriteArrayList

单线程的情况下,线程安全

package com.fang.unsafe;

import java.util.Arrays;
import java.util.List;

public class ListTest {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("1","2","3");
        list.forEach(System.out::println);
    }
}

JUC并发编程狂神说笔记(超详细)
出现并发修改异常

package com.fang.unsafe;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;
//java.util.ConcurrentModificationException 并发修改异常
public class ListTest {
    public static void main(String[] args) {
        //并发下ArrayList不安全
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();

        }
    }
}

解决办法:1.List list = new Vector<>();

2.集合工具类的使用List list = Collections.synchronizedList(new ArrayList<>());
3.List list = new CopyOnWriteArrayList<>();
CopyOnWrite:写入时复制,COW 计算机程序设计领域的优化策略。
多个线程调用的时候,list读取时固定,写入时覆盖
在写入时避免覆盖,造成数据问题
读写分离 mycat
CopyOnWriteArrayList比Vector好,
Vector这个用的是Sychronized,效率比CopyOnWriteArrayList低。
JUC并发编程狂神说笔记(超详细)

CopyOnWriteArraySet

package com.fang.unsafe;

import java.util.HashSet;
import java.util.UUID;

public class SetTest {
    public static void main(String[] args) {
        HashSet<Object> hashSet = new HashSet<>();
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                hashSet.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(hashSet);
            },String.valueOf(i)).start();
        }
    }
}

执行结果
JUC并发编程狂神说笔记(超详细)
解决办法
Set set = new CopyOnWriteArraySet<>();

hashSet底层是什么
底层是HashMap,set的add的方法本质就是map,key是无法重复的。

ConcurrentHashMap

JUC并发编程狂神说笔记(超详细)
解决办法
Map<String, String> map = new ConcurrentHashMap<>();

走进Callable

1.可以有返回值,可以抛出异常,方法不同,run(),/call()
代码测试

package callable;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class CallableTest {
    public static void main(String[] args) {
        new Thread().start();//怎么启动callable
        MyThread thread = new MyThread();
        FutureTask futureTask = new FutureTask(thread); //适配类
        new Thread(futureTask,"A").start();
        new Thread(futureTask,"B").start();//结果会被缓存,效率高
        try {
            String s = (String) futureTask.get();//callable的返回值,这个get方法可能会产生阻塞,把他放在最后
            //或者使用异步通信来处理
            System.out.println(s);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
}
class MyThread implements Callable<String> {
    @Override
    public String call() throws Exception {
        System.out.println("call");//会打印1个call
        return "1234";
    }
}

常用辅助类(必回)

CountDownLatch

public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        //总数是6
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 0; i < 6; i++) {
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"go out");
                countDownLatch.countDown();
            },String.valueOf(i)).start();
        }
        //等待计数器归零才会向下执行
        countDownLatch.await();
        countDownLatch.countDown();//-1
    }
}

6个线程都走完才会向下执行

CyclicBarrier

加法计数器

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierDemo {
    public static void main(String[] args) {
        //集齐七颗龙珠,召唤神龙
        //召唤龙珠
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7,()->{
            System.out.println("召唤神龙成功");
        });
        for (int i = 0; i <= 7; i++) {
            final int temp = i;
            //lambda不能直接拿到for循环中的i
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"收集"+temp);
                try {
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }).start();
        }
    }
}

JUC并发编程狂神说笔记(超详细)

Semaphore

抢车位

package add;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class SemaphoreDemo {
    public static void main(String[] args) {
        Semaphore semaphore = new Semaphore(3);
        for (int i = 1; i <= 6; i++) {
            new Thread(()->{
                //acquire()
                try {
                    semaphore.acquire();//获得,如果满了,会等待被释放为止
                    System.out.println(Thread.currentThread().getName()+"抢到车位");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName()+"离开车位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();//释放
                }
            },String.valueOf(i)).start();
        }
    }
}

JUC并发编程狂神说笔记(超详细)

ReadWritelock

实现类:ReetrantReadWritelock
读可以被多个线程同时读,写的时候只能有一个线程去写

package rw;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

//ReadWriteLock
public class ReadWriteLockDemo {
//    自定义缓存
    public static void main(String[] args) {
        MyCatchLock myCatch = new MyCatchLock();
//写入
        for (int i = 0; i <= 5; i++) {
            final int temp = i;
            new Thread(()->{
                myCatch.put(temp+"",temp+"");
            },String.valueOf(i)).start();
        }
        //读取
        for (int i = 0; i <=5; i++) {
            final int temp = i;
            new Thread(()->{
                myCatch.get(temp+"");
            },String.valueOf(i)).start();
        }
    }
}
class MyCatch {
    private volatile Map<String,Object> map = new HashMap<>(0);
    //存
    public void put(String key,Object value) {
        System.out.println(Thread.currentThread().getName()+"写入"+value);
        map.put(key, value);
        System.out.println(Thread.currentThread().getName()+"写入成功");
    }
    //取
    public void get(String key) {
        System.out.println(Thread.currentThread().getName()+"读取"+key);
        Object o = map.get(key);
        System.out.println(Thread.currentThread().getName()+"读取成功");
    }
}
//加锁的
class MyCatchLock {
    private volatile Map<String,Object> map = new HashMap<>(0);
    //读写锁更加细粒度的控制
    private ReadWriteLock lock = new ReentrantReadWriteLock();
    private Lock lock1 = new ReentrantLock();

    //存,写的时候,只希望同时有一个线程写
    public void put(String key,Object value) {
        lock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"写入"+value);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName()+"写入成功");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.writeLock().unlock();
        }
    }
    //取,读,所有的人都可以读
    public void get(String key) {
        lock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"读取"+key);
            Object o = map.get(key);
            System.out.println(Thread.currentThread().getName()+"读取成功");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.readLock().unlock();
        }
    }
}

JUC并发编程狂神说笔记(超详细)
独占锁(写锁) 一次只能被一个线程占有
共享锁(读锁) 可以同时被多个线程占有

阻塞队列BlockingQueue

写入:如果队列满了,就必须阻塞等待
取:如果队列是空的就必须阻塞等待生产

学会使用队列:四组api
1.抛出异常
2.不会抛出异常
3.阻塞等待
4.超时等待

方式 抛出异常 有返回值,不抛出异常 阻塞等待 超时等待
添加 add offer put offer(,)
移除 remove poll take poll(,)
判断队列首 element peek - -

抛出异常

public class Test {
    public static void main(String[] args) {
        //List,Set的父类Collection
        //BlockQueue不是新的东西继承自 Collection
//        什么情况下会使用阻塞队列:多线程并发处理,线程池
        test1();

    }
    public static void test1 () {
        //队列的大小
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        System.out.println(arrayBlockingQueue.add("a"));
        System.out.println(arrayBlockingQueue.add("b"));
        System.out.println(arrayBlockingQueue.add("c"));
         System.out.println(arrayBlockingQueue.element());//查看队首元素
        //ava.lang.IllegalStateException
        System.out.println(arrayBlockingQueue.add("d"));
        System.out.println("=============");
        //队列移除顺序
        System.out.println(arrayBlockingQueue.remove());
        System.out.println(arrayBlockingQueue.remove());
        System.out.println(arrayBlockingQueue.remove());
        //java.util.NoSuchElementException
        System.out.println(arrayBlockingQueue.remove());
    }
}

不抛出异常

JUC并发编程狂神说笔记(超详细)

    public static void test2 () {
        //队列的大小
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        System.out.println(arrayBlockingQueue.offer("a"));
        System.out.println(arrayBlockingQueue.offer("b"));
        System.out.println(arrayBlockingQueue.offer("c"));
        //ava.lang.IllegalStateException
        System.out.println(arrayBlockingQueue.offer("d"));
        System.out.println(arrayBlockingQueue.peek());
        System.out.println("=============");
        //队列移除顺序
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());

    }
}

等待阻塞(一直阻塞)

    public static void test3 () throws InterruptedException {
        //队列的大小
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        arrayBlockingQueue.put("a");
        arrayBlockingQueue.put("b");
        arrayBlockingQueue.put("c");
//        arrayBlockingQueue.put("d");队列没有位置,一直阻塞
        System.out.println("=============");
        //队列移除顺序
        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());//没有这个元素,一直阻塞
    }

等待阻塞(等待超时)

    public static void test4 () throws InterruptedException {
        //队列的大小
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        System.out.println(arrayBlockingQueue.offer("a"));
        System.out.println(arrayBlockingQueue.offer("b"));
        System.out.println(arrayBlockingQueue.offer("c"));
        //等待超过两秒退出
        arrayBlockingQueue.offer("d", 2,TimeUnit.SECONDS);
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        //等待超过两秒九退出
        System.out.println(arrayBlockingQueue.poll(2,TimeUnit.SECONDS));

同步队列SychronizedQueue

没有容量,进去一个元素,必须等待取出来之后,才能往里面再放一个元素
put,take

   public static void main(String[] args) {
        SynchronousQueue<Object> synchronousQueue = new SynchronousQueue<>();
        new Thread(()->{
            try {
                System.out.println(Thread.currentThread().getName()+"put 1");
                synchronousQueue.put("1");
                System.out.println(Thread.currentThread().getName()+"put 2");
                synchronousQueue.put("2");
                System.out.println(Thread.currentThread().getName()+"put 3");
                synchronousQueue.put("3");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"t1").start();
        new Thread(()->{
            try {
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+synchronousQueue.take());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"t2").start();

    }

JUC并发编程狂神说笔记(超详细)

线程池(重点)

池化技术及线程池的使用

程序的运行,本质:占用系统的资源!优化资源的使用
线程池,连接池,内存池,对象池
池化技术:事先准备好一些资源,有人要用就来拿,用完之后归还

线程池的好处
1.降低资源的消耗
2.提高响应速度
3.方便管理
线程可以复用,可以控制最大并发量,管理线程
线程池:三大方法,7大参数,4种拒绝策略

线程的三大方法

线程池不允许使用Executors去创建,而是通过ThreadPoolExecutor的方式,这样的处理方式让写的同学更加明确线程池的运行规则,规避资源耗尽的风险。 说明:Executors各个方法的弊端:
1)newFixedThreadPool和newSingleThreadExecutor:
  主要问题是堆积的请求处理队列可能会耗费非常大的内存,甚至OOM。
2)newCachedThreadPool和newScheduledThreadPool:
  主要问题是线程数最大数是Integer.MAX_VALUE(约为21亿),可能会创建数量非常多的线程,甚至OOM。

    public static void main(String[] args) {
        //Executors工具类,三大方法
        ExecutorService threadPool = Executors.newSingleThreadExecutor();//单个线程
        for (int i = 0; i < 10; i++) {
            //使用了线程池之后,使用线程池来创建线程
            threadPool.execute(()->{
                System.out.println(Thread.currentThread().getName()+"ok");
            });
        }
        //线程池用完,程序结束,关闭线程池
        try {
            threadPool.shutdown();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
        }
    }

JUC并发编程狂神说笔记(超详细)
//Executors工具类,三大方法
// ExecutorService threadPool = Executors.newSingleThreadExecutor();//单个线程
// ExecutorService threadPool = Executors.newFixedThreadPool(5);//创建一个固定大小得线程池
ExecutorService threadPool = Executors.newCachedThreadPool();//可伸缩,线程数可变

7大参数及自定义线程池

源码分析
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue()));
}
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue());
}
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue());
}
三大方法底层都调用得是ThreadPoolExecutor

//七个参数
    public ThreadPoolExecutor(int corePoolSize,//核心线程池大小
                              int maximumPoolSize,//最大核心线程大小
                              long keepAliveTime,//超时了没人用就会释放
                              TimeUnit unit,//超时单位
                              BlockingQueue<Runnable> workQueue,//阻塞队列
                              ThreadFactory threadFactory,//线程工厂,创建线程,一般不用动
                              RejectedExecutionHandler handler) {//拒绝策略
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

手动创建一个线程池
四种拒绝策略

JUC并发编程狂神说笔记(超详细)

 public static void main(String[] args) {
        //Executors工具类,三大方法
//        ExecutorService threadPool = Executors.newSingleThreadExecutor();//单个线程
//        ExecutorService threadPool = Executors.newFixedThreadPool(5);//创建一个固定大小得线程池
//        ExecutorService threadPool = Executors.newCachedThreadPool();//可伸缩,线程数可变
        //自定义线程池,工作
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2,
                5,
                3,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(3),
                Executors.defaultThreadFactory(),
//                new ThreadPoolExecutor.AbortPolicy()//银行满了还有人进来,不处理这个人,抛出异常
//                new ThreadPoolExecutor.DiscardPolicy()//队列满了不会抛出异常,丢掉任务
//                new ThreadPoolExecutor.CallerRunsPolicy()//哪里来的去哪里
                new ThreadPoolExecutor.DiscardOldestPolicy()//队列满了,尝试去和最早得竞争,也不会抛出异常
        );
        //最大承载:队列+max值
        for (int i = 0; i < 8; i++) {
            //使用了线程池之后,使用线程池来创建线程
            threadPoolExecutor.execute(()->{
                System.out.println(Thread.currentThread().getName()+"ok");
            });
        }
        //线程池用完,程序结束,关闭线程池
        try {
            threadPoolExecutor.shutdown();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
        }
    }

最大线程池应该如何定义
1.cpu密集行,12条线程同时执行,几核心就是几,可以保证cpu的效率最高
2.io密集型>判断你的程序中十分耗io的线程
程序 15个大型任务 io十分暂用资源
System.out.println(Runtime.getRuntime().availableProcessors());//获得cpu的核心数

四大函数是接口(重点)

新生代程序员:lambda表达式,链式编程,函数式接口,Steram流式计算
函数式接口:只有一个方法的接口//简化编程模型,在新版的框架中大量的应用
//foreach()参数消费者类型的函数式接口
代码测试:

函数型接口

JUC并发编程狂神说笔记(超详细)
传入T,返回R

    public static void main(String[] args) {
//        Function function = new Function<String,String>() {
//            @Override
//            public String apply(String str) {
//                return str;
//            }
//        };
        Function function = (str)->{return str;};
        System.out.println(function.apply("abc"));
    }

断定型接口

返回boolean值
JUC并发编程狂神说笔记(超详细)

    public static void main(String[] args) {
        //判断字符串是否为空
        Predicate<String> predicate = new Predicate<String>() {
            @Override
            public boolean test(String s) {
                return s.isEmpty();
            }
        };
        Predicate<String> predicate = (str)- >{return str.isEmpty();
        System.out.println(predicate.test(""));
    }

消费型接口和供给型接口

只有输入没有返回值
只有返回没有输入
JUC并发编程狂神说笔记(超详细)

Stream流式计算

存储+计算
存储:mysql,集合
计算都要交给流计算你

public class Test {
   public static void main(String[] args) {
       User user1 = new User(1,21,"张三");
       User user2 = new User(2,23,"李四");
       User user3 = new User(3,29,"王五");
       User user4 = new User(4,18,"赵六");
       //集合存储
       List<User> userList = Arrays.asList(user1, user2, user3, user4);
       //计算交给流
       userList.stream().filter(user -> {return user.getId()%2==0;})
               .filter(user -> {return user.getAge()>20;})
               .map(user -> {return user.getName().toUpperCase(Locale.ROOT);})
               .sorted((u1,u2)->{return u2.compareTo(u1); })
//                .limit(1)//分页
               .forEach(System.out::println);
   }
}

ForkJoin

什么是ForkJoin

ForkJoin在JDk1.7,并行执行任务!提高效率,数据量大!
大数据:Map Reduce把大任务拆分为小任务.
特点:

特点工作窃取

ForkJoin的操作

异步回调

Future的设计初衷:

    public static void main(String[] args) throws ExecutionException, InterruptedException {
//        //发起一个请求,没有返回值得异步回调
//        CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(()->{
//            try {
//                TimeUnit.SECONDS.sleep(2);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
//            System.out.println(Thread.currentThread().getName()+"run");
//        });
//        System.out.println("1111");
//        //获取阻塞执行结果
//        completableFuture.get();
       //有返回值的异步回调
       //ajax,成功和失败回调
       //返回的是错误信息
       CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(()->{
           System.out.println("completableFuture"+Thread.currentThread().getName());
           int i = 10/0;
           return 1024;
       });
       System.out.println(completableFuture.whenComplete((t, u) -> {
           System.out.println(t);//正常的返回结果
           System.out.println(u);//错误信息java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
       }).exceptionally((e) -> {
           System.out.println(e.getMessage());//java.lang.ArithmeticException: / by zero
           return 233;
       }).get());
   }

JMM

volatile是java虚拟机提供的轻量级的同步机制
1.保证可见性
2.不保证原子性
3.由于内存屏障,禁止指令重排
什么是JMM
JMM:java的内存模型,不存在的东西,概念,约定
关于JMM的一些同步的约定:
1.线程解锁前,必须把共享变量立刻刷回主存
2.线程枷锁前,必须读取主存中的最新值到工作的内存中
3.加锁和解锁是同一把锁
线程:工作内存 ,主内存
八种操作
???

    private static int num = 0;
   public static void main(String[] args) throws InterruptedException {//main线程
       new Thread(()->{//线程1
           while (num == 0) {

           }
       }).start();
       TimeUnit.SECONDS.sleep(1);
       num = 1;
       System.out.println(num);
       //程序一直在执行,线程1不知道主存中的值发生了变化
   }

Volatile

可见性

    //加了volatile可以保证可见性,不加进入死循环
   private volatile static int num = 0;
   public static void main(String[] args) throws InterruptedException {//main线程
       new Thread(()->{//线程1
           while (num == 0) {

           }
       }).start();
       TimeUnit.SECONDS.sleep(1);
       num = 1;
       System.out.println(num);
       //程序一直在执行,线程1不知道主存中的值发生了变化
   }

不保证原子性

原子性:不可分割
线程a在执行任务的时候,不能被打扰,也不能被分割,要么同时成功,要么同时失败

    private volatile static int num = 0;
    public static void add() {
        num++;
    }
    public static void main(String[] args) {
        //理论上num结果应该为20000,加volatile还是不能加到2万,加Synchronized可以
        for (int i = 0; i < 20; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    add();
                }
            }).start();
        }
        while (Thread.activeCount()>2) {
            Thread.yield();
        }
        System.out.println(Thread.currentThread().getName()+num);
    }

如果不加Synchronizd和Lock怎么保证原子性
num++;//不是原子性操作
JUC并发编程狂神说笔记(超详细)
使用原子类解决问题

    private volatile static AtomicInteger num = new AtomicInteger();
    public static void add() {
//        num++;
        num.getAndIncrement();//AtomicInteger+1方法CAS效率高
    }
    public void main(String[] args) {
        //理论上num结果应该为20000,加volatile还是不能加到2万,加Synchronized可以
        for (int i = 0; i < 20; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    add();
                }
            }).start();
        }
        while (Thread.activeCount()>2) {
            Thread.yield();
        }
        System.out.println(Thread.currentThread().getName()+num);
    }

这些类的底层都和操作系统挂钩,直接在内存中修改值,Unsafe类是一个很特殊的存在

指令重排

?你写的程序,计算机并不是按照你写的那样去执行
源代码->编译器优化->指令并行可能重排->内存系统可能重排->执行

int x=1;
int y=1;
x=x+5;
y=x+x;

我们期望的是1234,但是可能是21344,1324
不可能是4123,==处理器在执行指定重排的时候,考虑数据之间的依赖性
可能造成影响的结果x,y,a,b默认是0
volitale可以避免指令重排:
内存屏障.cpu指令.作用
1.保证特定的操作执行循序
2.可以保证某些变量的内存可见性(利用这些特性,保证valitale实现了可见性)

彻底玩转单例模式

饿汉式

package 单例模式;
//饿汉式单例
public class Hungry {
    //一上来就创建对象,可能会浪费空间
    private byte[] data1 = new byte[1024*1024];
    private byte[] data2 = new byte[1024*1024];
    private byte[] data3 = new byte[1024*1024];
    private byte[] data4 = new byte[1024*1024];
    private Hungry() {
    }
    private final static Hungry HUNGRY= new Hungry();
    public static Hungry getInstance() {
        return HUNGRY;
    }

}

DCL懒汉式

package 单例模式;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

//懒汉式单例模式
public class LazyMan {
    private static boolean qinjaing = false;

    private LazyMan() {
        System.out.println(Thread.currentThread().getName() + "ok");
        synchronized (LazyMan.class) {
//            if (lazyMan != null) {
//                throw new RuntimeException("不要试图用反射破坏异常");
        }
        if (qinjaing != false) {
            qinjaing = true;
        } else {
            throw new RuntimeException("不要试图用反射破坏异常");
        }
    }

    //单线程下确实单例ok
    private volatile static LazyMan lazyMan;

    //双重检测锁模式 懒汉式单例模式 DCL懒汉式
    public static LazyMan getInstance() {
        if (lazyMan == null) {
            synchronized (LazyMan.class) {
                if (lazyMan == null) {
                    lazyMan = new LazyMan();//不是原子性操作,
                    //1.分配内存空间
                    //2.执行构造方法,初始化对象
                    //3.把这个对象指向这个空间
                    //真实步骤可能执行132.此时lazyman还没被完成构造
                }
            }
        }

        return lazyMan;
    }
//    //多线程并发
//    public static void main(String[] args) {
//        for (int i = 0; i < 10; i++) {
//            new Thread(()->{
//                LazyMan.getInstance();
//            }).start();
//        }
//    }

//    //反射破解使其不安全,破坏单例
//    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
//        LazyMan instance = LazyMan.getInstance();
//        //获得无参构造器
//        Constructor<LazyMan> declaredConstructor = LazyMan.class.getDeclaredConstructor(null);
//        declaredConstructor.setAccessible(true);
//        LazyMan lazyMan = declaredConstructor.newInstance();
//        //单例模式.LazyMan@15fbaa4
//        //单例模式.LazyMan@1ee12a7
//        System.out.println(instance);
//        System.out.println(lazyMan);
//    }

    //两个对象都使用反射再次破坏单例模式
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException, NoSuchFieldException {
        //通过反射破坏标志位qinjiang
        Field qinjaing = LazyMan.class.getDeclaredField("qinjaing");
        qinjaing.setAccessible(true);

        //获得无参构造器
        Constructor<LazyMan> declaredConstructor = LazyMan.class.getDeclaredConstructor(null);
        declaredConstructor.setAccessible(true);
        LazyMan lazyMan = declaredConstructor.newInstance();

        //
        qinjaing.set(lazyMan,false);
        LazyMan instance = declaredConstructor.newInstance();
        //单例模式.LazyMan@15fbaa4
        //单例模式.LazyMan@1ee12a7
        System.out.println(instance);
        System.out.println(lazyMan);
    }
}

静态内部类

package 单例模式;
//静态内部类
public class Holder {
    private Holder() {

    }
    public static Holder getInstance() {
        return InnerClass.HOLDER;
    }
    public static class InnerClass {
        private static final Holder HOLDER = new Holder();
    }
}

单例不安全,因为有反射,所以使用枚举

package 单例模式;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

//enum是什么?本身也是一个class类
public enum EnumSingle {
    INSTANCE;
    public EnumSingle getInstance() {
        return INSTANCE;
    }
}
class Test{
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        EnumSingle enumSingle1 = EnumSingle.INSTANCE;
        //反射不能破坏枚举
//        EnumSingle enumSingle2 = EnumSingle.INSTANCE;
        Constructor<EnumSingle> declaredConstructor = EnumSingle.class.getDeclaredConstructor(String.class,int.class);
        declaredConstructor.setAccessible(true);
        EnumSingle enumSingle2 = declaredConstructor.newInstance();
        System.out.println(enumSingle1);
        System.out.println(enumSingle2);

        //Cannot reflectively create enum objects
        //	at java.lang.reflect.Constructor.newInstance(Constructor.java:417)
    }
}

深入理解CAS

什么是CAS

操作系统,计算机网络

JUC并发编程狂神说笔记(超详细)
JUC并发编程狂神说笔记(超详细)

Unsafe类

package cas;

import java.util.concurrent.atomic.AtomicInteger;

public class CASDemo {
    //CAS compareAndSet:比较并交换
    public static void main(String[] args) {
        AtomicInteger atomicInteger = new AtomicInteger(2020);
        //public final boolean compareAndSet(int expect, int update)
        //如果我期望的值达到了就更新,CAS是Cpu的并发原理
//        如果不是就一直循环,底层是自旋锁。
        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());

        System.out.println(atomicInteger.compareAndSet(2020, 2021));
        System.out.println(atomicInteger.get());
//        true
//        2021
//        false
//        2021
    }
}

CAS缺点
1.循环会耗时
2.一次性只能保证一个共享变量的原子性
3.引发ABA问题

原子引用解决ABA问题

ABA问题(狸猫换太子)

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